1. Field of the Invention
The present invention relates to a process for the purification of a gaseous organometallic compound. More particularly, it pertains to a process for the purification of a gaseous organometallic compound which process is capable of removing oxygen contained as an impurity in the gaseous organometallic compound down to a ultralow concentration.
Much importance is attached to the organometallic compounds each derived from a Ib, IIb or IIIb element of the Periodic Table, which compounds are typified by diethylzinc, trimethylaluminum, trimethylgallium, trimethylindium, dimethylgold acetylacetonato, etc., as they are used as raw materials for producing compound semiconductors such as zinc selenide (ZnSe), gallium-aresenic compound (GaAs) and indium-phosphorus compound (InP) and as wiring fabrication materials. In addition, such compounds as biscyclopentadienylmagnesium, tetramethyltin and dimethyltellurium increase their usage year by year as raw materials for doping. With the advanced performance of semiconductors in recent years, the above-mentioned raw materials are required to be ultralow in the content of impurities. 2. Description of the Related Art
With respect to the method for feeding an organometallic compound to be used during the production of a semiconductor, although diethylzinc is sometimes fed from a cylinder filled in with the gas thereof diluted with hydrogen or the like to 1% or less, there are usually available a method in which an organometallic compound is placed in a container such as a bottle one end of which is open to the air, the container is immersed in a thermostat and adjusted to an appropriate temperature and the resultant vapor of the organometallic compound is fed to a reactor while the flow rate of the vapor is controlled with a mass flow controller or the like, or a method in which an organometallic compound placed in a bubbler is subjected to bubbling by H.sub.2, N.sub.2 or He and the resultant vapor of the compound is fed to a reactor.
An organometallic compound usually contains oxygen, moisture and the like as impurities, of which moisture is removable by means of a dehumidifying agent such as zeolite.
The oxygen content in an organometallic compound is usually 10 ppm or less but in recent years there is available in the market the compound having a relatively low content of oxygen as low as 0.1 to 0.5 ppm.
Recently it has been made possible to highly purify arsine, phosphine and hydrogen selenide that are simultaneously used with an organometallic compound during the production of a compound semiconductor, enabling to lower an oxygen contained therein as an impurity to 0.01 ppm or less (refer to Japanese Patent Applicaiton Laid-Open No. 12303/1991, etc.). Under such circumstance the organometallic compound to be used therewith having an oxygen content of 0.01 ppm or less is eagerly desired.
In addition since the aforementioned organometallic compounds are sometimes contaminated with an impurity such as air mixing therein in the course of being fed to a semiconductor fabrication apparatus, for example, at the time of connecting a bottle, switching a pipeline or the like, it is desirable that the impurities be finally eliminated immediately before feeding to the apparatus. The demand for a highly purified organometallic compound continues to increase year by year. Nevertheless there is hardly found a publicly known technique capable of efficiently removing oxygen contained in organometallic compounds.
In view of the aforesaid situation intensive research was concentrated by the present inventors on a process for efficiently removing oxygen contained in organometallic compounds down to a ultralow level. As a result it has been discovered that the oxygen contained therein can be removed as low as 0.1 ppm and further 0.01 ppm by bringing an organometallic compound into contact with a specific catalyst comprising copper or nickel as the essential ingredient. The present invention has been accomplished on the basis of the above-mentioned finding and information.